Thank you for getting in touch. Here is the 3.21 changelog:
3.21 :- 2020-04-07 :- Medium priority
* Dropped call to deprecated function wpgmaps_filter
* Fixed only one category assigned to submitted markers when multiple categories have been selected by the user
* Fixed custom field data not being submitted
We’ve updated the “tested up to” string on our update server as well, thank you for pointing that out.